Cathode assembly



March 23, 1965 J. M. DREES ETAL CATHODE AS SEMBLY 2 Sheets-Sheet 1 Filed Aug. 25, 1960 INVENTORS JOSEPH M. DR EES DONALD c. KELSEY 00mm c c. MERCURIO BY aux/l0 ATTORNEY March 23, 1965 J. M. DREES ETAL CATHODE ASSEMBLY 2 Sheets-Sheet 2 Filed Aug. 25, 1960 INVENTORS JOSEPH M. DREES DONALD C. KELSEY DOMINIC BY (flMA MERCURIO TTORNEY United States Fatent Gfilice 175,115 Patented Mar. 23, 1965 3,175,115 CATHODE ASSEMBLY Joseph M. Drees, Saratoga, Donald C. Kelsey, Santa Clara, and Dominic C. Mercurio, San Jose, Calif., assignors to Sylvania Electric Products Inc., a corporation of Delaware Filed Aug. 25, 1960, Ser. No. 51,962 6 Claims. (Cl. 31382) This invention relates to the manufacture of electron guns and particularly to an improved mount for the cathode and focus electrode of such guns.

The conventional electron gun usually includes a cathode, heater, focus electrode, and one or more accelerating electrodes mounted in precise axial and radial locations on and about the axis of symmetry of an electron discharge tube. As electrons are emitted from the cathode, a columnar beam is formed, focused and accelerated along a predetermined path by electrostatic forces derived from electrical and mechanical characteristics of the focus and accelerating electrodes.

In the past, in order to attain precise alignment and spacing of the cathode and focus electrode (the parts which form and focus the electron beam), costly and intricate manufacturing procedures were used. This has been particularly true in the manufacture of velocitymodulated tubes which depend on high-density, long tubular electron beams for their characteristics. Specifically, it has been the practice to use mechanical spacers to determine the aforementioned axial and radial spacing of the cathode and focus electrode, that is, to determine the axial distance between the thermocmissive coating on the cathode and the aperture of the focus electrode, and the alignment of the axes of the cathode and focus electrode (concentricity). The allowable variation in these dimensions, in the order of 0.0015 and 0.004 inch, respectively, has necessitated selective assembly of the spacers and the cathode and focus electrode sub-assemblies, a time-consuming and costly operation.

According to the present invention, selective fit of parts is eliminated, enabling the cathode and focus electrode assembly to be manufactured with greatly improved uniformity, greater accuracy and lower cost. In particular, the present invention permits spacing and concentricity to be relatively independent of the tolerances of individual parts of the assembly because the cathode mount is designed to allow last minute adjustments before permanent mounting takes place. This mount comprises a conventional cylindriml cathode, having a spherical-shaped protuberance or pivot ring formed on its exterior surface. Whenthe cathode is coaxially mounted within the cylindrical support member of a focus electrode sub-assembly, tangential contact is made between the ring and the interior surface of the support.

The point-contact between the ring and support allows pivotal movement of the end of the cathode containing the thermo-emissive coating until precise concentricity of the cathode and aperture of the focus electrode is obtained. In addition, only small forces are needed to move the cathode in the axial direction to obtain correct axial spacing between the several parts. Welds applied at the line of contact of the pivot ring with the enclosing cylinder permanently secure the cathode relative to the focus electrode.

It is therefore a general object of this invention to provide an improved cathode and focus electrode assembly wherein the spacing and the concentricity of component parts are obtained without the use of separate mechanical spacers.

Another object is to provide an improved cathode and focus electrode assembly which has a minimum number of parts and therefore is more economical to manufacture.

A further object is to provide an improved method of aligning an electron gun assembly by which critical cathode and focus electrode spacing and concentricity are achieved rapidly and with increased accuracy.

These and other objects of the invention will become apparent from the following description of a preferred embodiment thereof shown in the accompanying drawings in which:

FIGURE 1 is a partially schematic longitudinal section of a traveling wave tube embodying the invention;

FIGURE 2 is a transverse section of the gun structure taken on line 22 of FIGURE 1 showing the radial position of the parts; and

FIGURE 3 is a longitudinal section of a cathode and focus electrode assembly taken on line 3+3 of FIGURE 2 showing the relationship of assembled parts, and, in addition, illustrating the apparatus used in aligning and welding parts of the assembly.

A preferred embodiment of the invention is illustrated in FIGURE 1 as a traveling wave tube comprising an elongated glass envelope 1 having enlarged end portion 2 enclosing the gun structure 3 of the tube. A cathode in the gun structure produces an electron beam which is focused and accelerated along tube axis A through helix 5 to collector 7 at the opposite end of the tube. The electrons interact in a well-known manner with electromagnetic waves on the helix so that a signal applied to the input 8 is amplified when it appears at the output 9. The efhciency of the tube depends in large measure on the axial travel of the electrons through the helix 5 and a contributing factor in achieving this type of flow is a precisely formed and assembled gun structure. This invention concerns such a gun structure and its method of assembly.

In accordance with the invention, a cathode mount generally indicated at 10 in FIGURES 1 and 3, comprises a cathode sub-assembly 4 mounted within a focus electrode sub-assembly 34. For convenience in describing this invention, the term cathode sub-assembly is used in this specification to describe not only the electron emitting body, but also the entire supporting structure formed thereto. Likewise, the term focus electrode sub-assembly, used herein, refers to the focus electrode, and its support structure.

Accordingly, focus electrode sub-assembly 34 comprises a cylindrically shaped focus electrode 11 having a re-entrant forward end wall 12 formed with a central aperture 13. The term forward, as used herein, describes the end of the assembly from which electrons are emitted and refers to the upper end of the structure in FIGURE 3; and similar, rear, rearward, or aft refers to the opposite or lower end of the structure.

Electrode 11 is supported concentrically of axis 14 of the assembly, which axis is coincident with tube axis A, by pairs of radial posts 15 secured to the exterior of the electrode and to longitudinally extending insulators 16 which in turn are supported at their rearward ends by pairs of radial posts 17, and elongated input leads 18. Leads 18 extend through and are supported on the base 19 of glass envelope 1.

Mounted to lower posts 17 concentrically of axis 14 is a tubular support member 20 having a thick walled upper part 21 and a thin walled lower portion 22, with shoulder 36 formed therebetween. Portion 22 is adapted to be ber 23 also has a forwardly and inwardly tapering interior surface 28at its rear end to removably receive the head of an adjusting tool as will be explained below. The outside diameters of the pivot ring 24, central-portion 25 and forward portion 26 are successively reduced, so that the .ipivotring is adapted to engage the interior of support member to permit pivotal movement of the sleeve about axes in a plane normal to the axis 14 of the assembly. The minimum area contact between pivot ring 24 and member 20 also facilitates axial (forward and rearward) adjustment of the sleeve.

Supported on theexterior surfaces of central portion 25 and of forward portion 26 of member 23 and concentrically of axis 14 are forwardly extending coaxial outer and inner tubular heat shields 29 and 30, respectively.

Both heat shields 29 and 30 extend beyond the front end of the sleeve member 23, with inner shield 30 supporting an upper cathode sleeve 31 at its forward end. Specifically,;the forward end of the inner shield is secured to a collar 32 on an elongated tubular housing 33 in the lower portion of which is found an enclosure for a heater and in the upper end of which is mounted an electron emission body 35. The upper ends of shields 2? and 30 preferably are flush with each other, and the radial spacing between the shields insulates the cathode sub-assembly thereby reducing conductive and radiant heat losses during tube operation. The outside diameter of the lower part of housing'33 is less than that of the inner shield 30 so an additional annular space is formed to further insulate against heat loss. When a heater is installed, leads 40 e'xtenddown to the base 19, see FIGURE 1, through tubular member 23 for connection.

The source of electrons in the cathode is a body 35 made, for example, of barium oxide impregnated in sintered tungsten. The diameter of the upper :part of the body 35 is reduced to form a cylindrical button 43, and the upper surface 44 of the shoulder is suitably coated to prevent emission of electrons so that electrons are emitted only from the extreme upper surface 45 of button 43.

The relative axial and lateral positions of button surface 45 and the aperture 13 in focus electrode end wall 12 are extremely critical and must be precisely controlled in order to insureproper formation of the electron beam. Adjustment of theposition of button surface 45 relative to electrode aperture 13in the focus electrode end wall is accomplished by means of pivot ring 24 at the rear end of sleeve 23. This ball-in-sleeve connection allows pivot ing of cathode button 43 about the center of formation of thepivot ring. The concentricity of button surface 45 and aperture 13 may be quickly and conveniently achieved to an accuracy in the order of i0.001 inch in the button to aperture edge spacing 48. The minimum contact area between the pivot ring and the interior of support member 20 facilitates forward and rearward adjustment of surface 45 relative to edge 47 of the aperture to obtain precise axial spacing of these parts as indicated at 49 in FIGURE 3, so that variations not exceeding $00005 inch can be achieved. After axial and lateral adjustments or thecathode are completed, the parts are permanently secured in the final position preferably by welds '50 applied at the place of contact of the pivot ring and the interior walls of'support member 20. The completed cathode-focus electrode assembly 10 is then mounted within tubular anode assembly 6 and electrical connections made to form gun structure '3.

Among the advantages of the described cathode mount areease of manufacturing, low cost, and greater accuracy in alignment of parts. By way of example, a cathode l mount embodying this invention and having the following dimensions, has been constructed and successfully tested:

Item Dimensions Focus Electrode Sub-assembly 34" Aperture 13 Support Member 20..

Overall length 0.820.

Diameter 0.045. Mean Diameter 0.23, Length 0.400. Diameter 0.400, Length Mean Diameter 0.15,

Focus Electrode 11 Insulators l6 Length 0.56.

Post 15 Diameter 0.040, Length Tower Post 17 Diarge ter 0.040, Length Leads 18 Diameter 0.040, Length Overall length osso".

Diameter 0.080, Length Mean Diameter 0.140,

Length 0.280".

Mean Diameter 0.180,

Length 0.400.

Mean Diameter 0150,

Length 0.325.

Mean Diameter 0.150,

Length 0.500.

Diameter (outside) 0.200",

Length 0.11.

Cathode Subhssembly 4 Cathode Button 43 Upper Cathode Sleeve 31 Heat Shield 29 Heat Shield 30 Sleeve Member 23 Pivot Ring 24 As listed above, the term cathode sub-assembly describes the electron emitting body 35 and the entire supporting structure, i.e., upper cathode mount 31, heat shields 29, 30 and sleeve member 23. Similarly, the term focus electrode sub-assembly refers to focus electrode 11 and its support structure including radial posts 15, '17, insulators 16, input leads 1'8, and support memberZil.

The method by which the cathode sub-assembly is aligned relative to the focus electrode sub-assembly, will now be described by reference to FIGURES 2 and 3. It should be noted that the following description'omits details by which the above sub-assemblies are fabricated. It is sufficient to point out that mechanical fixtures have'been adapted to permanently mount the integral parts of these subassemblies in accurate axial and radial locations as required in the art. After which, the cathode and focus electrode sub-assemblies are mounted in a mechanical jig or fixture 51. In the upper portion of this jig, the focus electrode sub-assembly is supported in fixed'horizontal and radial locations, while the cathode sub-assembly is supported in the lower portion on adjustable support means.

In the upper portion, focus electrode sub-assembly 34 is supported by a press fit between upper portion 21 of support member 20 and housing shell 52 of fixture 51. An annular protuberance (not shown) extending inwardly from the interior surface of housing shell 52 supports shoulder 36 of support 20 locating'the focuselectrode subassembly in a fixed horizontal plane. The supporting means of this sub-assembly is accurately formed so the axis of symmetry of the jig and sub-assembly are aligned.

The lower portion of housing shell 52 is appropriately formed to support the cathode sub-assembly relative to the focused electrode sub-assembly, as will be explained below. Sleeve member 23 of the cathode sub-assembly 4 has an inwardly tapered interior surface 28 for removably receiving the outwardly tapering surface 53 of guide pin 54. Pin 54 is characterized by the aforementioned surface in its frontal portion, and successively reduced middle and aft portions with shoulders 55 and 56 formed between respective portions. Support of pin 54 (and hence the cathode sub-assembly) is achieved by coaxially mounted annulus 57 having an upper surface 58 abutting shoulder 55 of pin 54, and in turn, supported by adjustable intermediate support members 62 mounted to the housing shell 52. Interior wall'sur faces 6 0 of annulus 57 snugly fits the mating exterior wall surface of the middle portion of pin 54. With little interplay therebetween, lateral movement of one is directly transmitted to the other.

The end terminating surface of ring 57 has an outwardly truncated spherical end wall 61 which snugly receives the inwardly truncated spherical end wall 59 of intermediate cylindrical support member 62. This arrangement resembles two cylinders mounted end-to-end, a differentiating characteristic being that the end edge surfaces of the annulus and member 62 are of a spherical nature. Edge contact of the parts also allow direct transfer of axial movements of one to the other. Upward movement of support member 62 is directly transmitted to annulus 57 and thereafter to the cathode sub-assembly. Conversely, downward movement of support 62 results in downward movement of the annulus (and cathode subassembly).

Adjacent to exterior walls 63 of annulus 57 are three adjusting screws 64 mounted to the shell housing, the ends of which bear against the exterior walls of the annulus. As the screws are rotated, in sequence, one inwardly of the annulus, the others outwardly, movement of the annulus relative to support member 62 is initiated. This relative movement is transmitted by the annulus to pin 54, and thereafter to the cathode sub-assembly. It is, however, not in the same plane as that of the screws, being pivotal about a point above this plane, called the center of formation, referenced at 65 in FIGURE 3, at the intersection of axes 14 and 66. That is, as the screws are rotated, the annulus follows the contour of the surface of end wall 61 and its mating surface '59 of support 62, which pivots its axis of symmetry in relation of that of the fixture. This pivotal movement is transmitted to pin 54 so like movement of the assembly about the center of formation 65 in a plane normal to axis 14 occurs.

It is noted that the outer surfaces of pivot ring 24 and button 43 of the cathode sub-assembly, and the mating surface of annulus 57 and its cylindrical counterpart, support 62, have the identical center of formation 65. Thus, pivotal movement of pin 54 is transmitted by pivot ring 2 4 to button 43, to pivot the button relative to the aperture 13 about the axis through the center of formation normal to axis 14. Radial adjustment of the button and aperture to obtain concentricity in the button-toaper-ture edge spacing 48 is thus easily achieved.

The pivot-a1 motion of the cathode button 43 and pin 54 is analogous to the relative motion of a teeter-totter or seesaw except the motion is producible into any radial direction in the plane normal to axis 14. If the analogy is taken further, an end of the seesaw would be occupied by button 43, the fulcrum would be pivot ring 24 and the initiating force being transmitted by screws 64 through annulus 57 to pin 54 near the other end.

The outside diameter of the aft portion of guide pin 54 is reduced so that the coaxially located, adjoining surfaces of the downwardly extending lower support 62 do not meet as tilting of the cathode sub-assembly takes place.

After correct concentricity is achieved, precise axial spacing between edge 47 of the aperture and surface 45 of the electron emitting body of the cathode, referenced at 49 in FIGURE 3, is desirable. Since axial movement of intermediate support 62 is transmitted through shoulder supporting surfaces of annulus 57 to pin 54 and thereafter to the cathode, spacing of parts is achieved by axial movement of this member relative to the housing shell, the supporting member of the aperture.

Support 62 has threads 67 formed on its exterior surface to which is attached a retaining nut 68. The nut is supported in the fixture between bearings 69, 7 by fingers 71 of the housing shell. Openings 72 through the housing shell permits rotation of the nut by an operator to move support 62 relative to the housing shell. When not 68 is rotated, support 62 moves axially (either forward or rearward) by thread engagement, the threads of the nut with those formed on the exterior surface of support 62. Since the entire cathode sub-assembly is supported by member 62, axial movement of the sub-assembly is then achieved easily, quickly and to a high degree of accuracy.

The terminating end of pin 54 (not shown) coaxial with support 62 is fitted with a grounding cable which is connected to a terminal of an appropriate energizing means to weld the cathode and focus electrode sub-assemblies. The other terminal is connected to welding electrodes 73 attached to the cylindrical shell 52 in the central portion of the assembly. After axial and radial adjustments are completed, welds are applied by means of the aforementioned energizing circuit at the place of contact of the pivot ring and the interior wall of support member 20 to complete the assembly.

Having thus described the vehicle for facilitating axial and radial adjustments of the referenced parts, the stepby-step attainment of these invention objects is hereinafter presented.

Axial spacing of sub-assemblies is attained using a toolmakers optical microscope which measures the spacing 4? between the emitting surface 45 and edge 47 of aperture 12. The microscope comprises eyepiece and objective lenses in an appropriate housing mounted to a fixed vertical support post, means for moving the housing relative thereto, and a fixed base mounted to the support post upon which the object to be viewed is supported. The ob-. jective lens has a very short focal length so objects spaced minute distances from one another (i.e., on edge of the aperture and surface 45) can be differentiated. The image of the aperture edge 47 is then brought into focus by adjusting the distance between the object and the objective lens by moving the scope relative to its base. This distance must be precise to obtain the sharpest image possible. The lenses are then re-adjusted to focus on a surface in a plane a specific axial distance therefrom. This distance is measured by a dial indicator mounted to the fixed vertical post with the stem of the indicator contacting the microscope. As viewed in FIGURE 2, the readjustment would be in the downward direction from a plane at the surface of the figure to a plane below. If the image of surface 45 of the cathode button is not in clear focus after the microscope is adjusted, the button must be re-located to obtain a clear image. This adjustment may be a downward or upward direction and is accomplished by rotating nut 68 mounted to support 62 in a clockwise or counterclockwise direction which, as previously mentioned, moves the emitting surface 45 of the cathode button relative to the aperture until the emitting surface is in clear focus when viewed in the scope.

Variation in the spacing of the parts by this described method have been found to be within 0.0005 incha threefold improvement over prior art methods.

Concentricity of emitting surface 45 and aperture 13 is also best measured by a toolmakers microscope. One particularly adaptable microscope comprises an objective lens with wider angle and longer focal length than that used in the spacing sequence described above and having a cross-hair and indexing reticle located in the focus of the eyepiece wherein the cross-hair is downwardly focused on the end edge of the aperture, and the distance observed between this edge and that of the emitting surface by counting the number ofindices or lines separating the edges. The longer focal length of the objective lens allows these edges to be observed simultaneously by the operator. This measuring technique is then repeated at four points degrees apart on the aperture. If adjustment of the radial position (concentricity) of the subassemblies is needed, adjusting screws 64 are rotated, forcing annulus 57 to be moved horizontally. As previously mentioned, the horizontal movement is transcribed into pivotable motion of the cathode sub-assembly relative to the focus electrode sub-assembly. The measuring technique is continued until button to edge spacing 48 is constant within 0.001 inch variation when sequentially measured at four points 90 degrees apart-a four-fold increase over prior art means.

When correct axial and radial spacings of emitting surface 45 and aperture 13 are obtained, welds 58 are circumferentially applied at the intersection of the surfaces of pivot ring 24 and lower portion 22 of support 20. It will be noted that the reduced wall thickness of portion 22 allows-fusion of the aforementioned parts at a lower temperature than would be possible using a straight tubular member. In addition, this wall is resilient which allows flexing when pressure is applied by electrode '73. This reduction of diameter allows a reduced portion thereof to contact the pivot ring and thus facilitates welding of the parts without a precise radial fit. Welding electrodes 73 and pin 54 are then withdrawn from portion 22 and sleeve member 23, respectively, after which the completed cathode-focus electrode is removed from the fixture.

It should be understood that this invention in its broadest aspects is not limited to the specific example herein illustrated and described, and that the following claims are intended to include all changes and modifications within the true spirit and scope of the invention.

We claim:

1. A cathode mount having an axis and comprising, in combination, a focus electrode sub-assembly having a coaxiallydisposed tubular focus electrode and a coaxial support member, said focus electrode having a re-entrant 'end wall with a central opening therein, and means to suppont said focus electrode and support member in a fixed relationship with each other; and a cathode subassembly comprising an electron-emitting body symmetrical of said axis and first and second support sleeves, means for securing said body on one end of the first support sleeve adjacent to the focus electrode, means for securing the first support sleeve to the second support sleeve, said second sleeve having a spherically shaped ring portion disposed within and engaging said support member of the portion of said sleeve engaging said support member, and means to secure said member to said protuberance. V

3. Structure according to claim 2 in which said focus electrode has an end wall with a coaxial opening therein, and electron emitting means on said one end portion of said sleeve aligned with said opening.

4. A cathode assembly comprising a focus electrode having an axis, a first sleeve member axially spaced from said electrode and having an axis aligned with the electrode axis, means for supporting said electrode and said member in fixed relationship to each other, a second sleeve member disposed coaxially within and extending from said first sleeve member toward said electrode, and a cathode body supported on said second member and disposed adiacent to said electrode, said second member having a spherically shaped ring portion axially remote from the cathode body and secured to the interior of said first member.

5. A cathode mount as defined in claim 1 in which said cathode sub-assembly has an axis coincident with the mount axis and said means for securing the first support sleeve to the second support sleeve comprise outer and inner coextensive radially spaced tubular shields, adjacent ends of said shields being attached to the second sleeve, the opposite end of said inner shield being connected to the first support sleeve.

6. A cathode assembly comprising an electrode having an axis, a tubular support member having a portion axially spaced from said electrode, means for securing said electrode and said support member in relatively fixed relationship, a sleeve member disposed within said support member, and an electron emitter supported on said sleeve member adjacent to said electrode, said sleeve member having a spherical protuberance thereon permanently secured to said portion of said support member.

References Cited by the Examiner UNITED STATES PATENTS 2,568,631 9/51 Hoellerich.

2,793,312 5/57 Hangen et al. 313-82 2,828,433 5/58 Frenkel 31382 2,845,690 8/58 Harrison 2925.l4 2,869,217 1/59 Saunders 29-25.14

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner. 

1. A CATHODE MOUNT HAVING AN AXIS AND COMPRISING, IN COMBINATION, A FOCUS ELECTRODE SUB-ASSEMBLY HAVING A COAXIALLY DISPOSED TUBULAR FOCUS ELECTROD AND A COAXIAL SUPPORT MEMBER, SAID FOCUS ELECTRODE HAVING A RE-ENTRANT END WALL WITH A CENTRAL OPENING THEREIN, AND MEANS TO SUPPORT SAID FOCUS ELECTRODE AND SUPPORT MEMBER IN A FIXED RELATIONSHIP WITH EACH OTHER; AND A CATHODE SUBASSEMBLY COMPRISING AN ELECTRON-EMITTING BODY SYMMETRICAL OF SAID AXIS AND FIRST AND SECOND SUPPORT SLEEVES, MEANS FOR SECURING SAID BODY ON ONE END OF THE FIRST SUPPORT SLEEVE ADJACENT TO THE FOCUS ELECTRODE, MEANS FOR SECURING THE FIRST SUPPORT SLEEVE TO THE SECOND SUPPORT SLEEVE, SAID SECOND SLEEVE HAVING A SPHERICALLY SHAPED RING PORTION DISPOSED WITHIN AND ENGAGING SAID SUPPORT MEMBER OF THE FOCUS ELECTRODE SUB-ASSEMBLY, AND MEANS FOR SECURING SAID 